Magnetic Isotope Effect of Magnesium in Phosphoglycerate Kinase Phosphorylation

Phosphoglycerate kinase (PGK) is found to be controlled by a25Mg2+-related magnetic isotope effect. Mg2+nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure25Mg2+(nuclear spin 5/2, magnetic moment +0.85) and24Mg2+(spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of25Mg2+, ATP production is 2.6 times higher compared with the yield of ATP reached in24Mg2+-containing PGK-based catalytic systems. The chemical mechanism of this phenomenon is discussed. A key element of the mechanism proposed is a nonradical pair formation in which25Mg+radical cation and phosphate oxyradical are involved.